can not get access to hardware virtualisation and runs on software virtualisation. Now that your Hyper-V has got the hardware virtualisation feature, i think you could be using both hypervisors at the same time and that may be why VBox can not get the hardware virtualisation.

Do not run other hypervisors (open-source or commercial virtualization products) together with VirtualBox! While several hypervisors can normally be installed in parallel, do not attempt to run several virtual machines from competing hypervisors at the same time. VirtualBox cannot track what another hypervisor is currently attempting to do on the same host, and especially if several products attempt to use hardware virtualization features such as VT-x, this can crash the entire host.

Just to exclude Hyper-V, run the benchmark twice. Once with VT-x/AMD-V enabled in the VM settings, and once with it disabled. You should see the same performance drop, about 20 times. If the performance with VT-x/AMD-V turned off is faster than when it was with Hyper-V installed, it means it was 'fighting' with Hyper-V to get CPU access as a hypervisor.